Many people may have heard of Aluminum Phosphide (AlP) and its use as a pesticide, but very few may be aware of its applications as a semiconductor material. In this blog post, we’ll discuss AlP semiconductor materials, what they are and why they’re so important. We’ll also delve into their band structures, their electrical as well as optical properties, and common applications of AlP materials from light-emitting diodes to lasers. Whether you’re just getting acquainted with semiconductors or looking to brush up on your understanding of these essential building blocks of electronics, read on!
Direct Band Gap Vs Indirect Band Gap
Before we get into Aluminum Phosphide and its unique structural and electronic properties, let’s take a brief look at the energy gaps in semiconducting materials that make these possible. The band gap is an important aspect of all semiconductors, and it refers to the energy gap that exists between the conduction band and the valence band where the material’s electrons are distributed. Each material has its own band structure and a unique band gap energy.
A band gap’s size indicates how much energy is needed to excite electrons from the valence band, where electrons are normally at rest, to the conduction band, where they move freely and cause an electrical current. In semiconductors, band gaps may be either direct or indirect depending on where the electron jumps from to become a free-moving electron.
For semiconducting materials with direct band gaps, electrons jump from one band directly, which means that recombination with holes can take place quickly, allowing them to emit photons easily. This makes these types of materials ideal for light-emitting applications like LEDs and lasers.
Indirect band gap materials require electrons to make a slight detour before becoming free. They have to pass through an intermediate state and transfer some momentum to the lattice structure based on their lattice constant value. This results in slower motion of charge carriers when compared to direct band gap materials. While they are unable to emit photons, they do often possess other desirable properties useful in different applications.
Aluminum Phosphide (AlP) much like Silicon, which is another widely used semiconducting material has indirect band gaps. This would indicate that it is incapable of being used for technology that relies on optical characteristics. However, as we will see later, AlP’s composition can be modified by alloying it with other elements. This is possible for many group III-V elements including AlP, making the resulting compound semiconducting material useful in optoelectronic applications.
AlP is also what is known as a wide band gap semiconductor. While a regular semiconducting material like Silicon has energy haps in the 0.6 to 1.5 eV (electronvolt) range, a wide gap material like AlP has a gap of about 2.45 eV. Wide-gap semiconducting materials exhibit different properties such as high thermal conductivity, allowing them to be used at higher temperatures where traditional materials fail to operate.
Additionally, wide-gap semiconducting materials are also known for their ability to function at higher voltages and radio frequencies, making them very useful in military applications. AlP is not the only Aluminum-based material used by the semiconducting industry, with its relatives like Aluminum Nitride (AlN) also being utilized in the manufacture of optoelectronics.
The Geometric Structure And Physical Properties Of AlP
Aluminum Phosphide has a Zinc Blende structure which means that the ions of the crystalline structure are in a cubic arrangement similar. The name comes from the mineral Zinc Blende also known as sphalerite which is a form of Zinc Sulfide (ZnS). It is the lattice constant of AlP which has a value of 5.4510 Å at 300 K that describes the physical properties like the angles and dimensions which determine how the unit cells of the crystalline structure are arranged. Furthermore, the crystalline structure also affects the thermal conductivity of the material.
The lattice constant also factors into the band gaps. For instance, compound semiconducting materials are formed by matching lattice structures with similar lattice constants. This allows the band gap to be modified without compromising the structural aspects of the crystal system.
How The Electronic And Optical Properties Of Aluminum Phosphide Are Obtained
The absorption coefficient and refractive index of a semiconducting material are what determine its optical properties. Furthermore, the charge carrier density plays an important role in determining its electronic properties. These values can be modified by changing the composition of AlP. This is done by alloying it with other materials to obtain compound semiconducting materials like Aluminum Gallium Indium Phosphide (AlGaInP).
AlGaInP is produced through a process called heteroepitaxy, which is used to grow crystalline layers of one compound on top of a seed layer or substrate made from another compound. The resulting crystalline structure of AlGaInP is also Zinc Blende. The band gap is calculated to lie between 1.81 eV to 2 eV. Since these energies correspond to frequencies in the deep ultraviolet to infrared, this determines the type of optoelectronic devices they are used to build.
Potential Applications Of Aluminum Phosphide
Here are some of the applications of Aluminum Phosphide and other compound materials made from it.
Light-Emitting Diodes
Due to AlP’s optical properties, light-emitting diodes (LEDs) are the most widely used application. LEDs made from AlGaInP specifically are known for their high brightness with the most commonly used colors being red, yellow, orange, and green.
Diode Lasers
Diode lasers are another type of device made from AlGaInP. Similar to an LED, this type of device relies on a p-n junction as well. Depending on the choice of semiconducting material, lasers can emit light from infrared to ultraviolet. AlGaInP specifically falls into the visible and near-infrared wavelengths. Optical disc readers such as DVD and Blu-Ray players, as well as gas sensors, laser scanners, laser printers, and laser pointers, are all made from this type of material.
High-Frequency Applications
Due to the wide gap qualities, Aluminum Phosphide is often used in high-power and high-frequency applications. Details remain sparse, but powerful military radar systems are said to include this material in their construction.
Quantum Wells
Getting back briefly to AlGaInP, the development of quantum well structures using this material enables all sorts of innovations from better performance in laser diodes, to high electron mobility transistors, and photodetectors. Quantum well technology could eventually replace conventional electronic components, improving their speed of operation, especially in the field of telecommunications.
Solar Cells
Image taken from www.newatlas.com
AlGaInP using the quantum well methods also shows much promise to raise the efficiency of solar cells up to about 40%. While this is still theoretical, the next generation of multi-junction solar cells designed with a five-junction structure and high Aluminum composition could prove to be a massive improvement in photovoltaic technology, far exceeding the efficiencies possible today.
Pesticides
Apart from its many uses in the semiconducting industry, Aluminum Phosphide is used as a pesticide. For example, it is can be used to get rid of everything from rodents to insects. It can also be used as a fumigant to kill harmful bacteria when storing grain in silos or transport containers.
The Future Of AlP-based Semiconducting Materials
AlP is toxic if ingested and may even pose a fire hazard, although these concerns are mainly in the agricultural field. In the world of semiconductors, there is much innovation that is possible through AlP-based materials. The next generation of quantum well structures and solar cells are showing much potential, and LEDs as well as diode lasers continue to be used in many of our modern consumer electronics devices. To learn more about semiconducting materials, manufacturing methods, and manufacturing equipment, visit Inquivix Technologies
FAQs
Yes. Aluminum Phosphide is a wide-gap semiconducting material that is used in the manufacture of components like light-emitting diodes, laser diodes and high-frequency radar systems.
Aluminum Phosphide or AlP has an indirect band gap which normally prevents it from exhibiting optical characteristics. However, by using AlP to make Aluminum Gallium Indium Phosphide or AlGaInP, semiconducting devices that emit or detect light can be manufactured
